1. Field of the Invention
The present invention relates to a vehicle-use brake device which is used for a vehicle such as a motorcycle.
2. Description of Background Art
A brake device for a motorcycle has been developed that is referred to as a by-wire-method which electrically detects a manipulated variable of a brake manipulation portion such as a brake lever or a brake pedal by a sensor, generates a liquid pressure by a hydraulic modulator which is electrically driven based on a detection value, and applies the liquid pressure to a brake caliper. This method is hereinafter, referred to as “by-wire method.” See, for example, JP-A-2005-212677.
In such a brake device, a master cylinder, which is interlockingly operated with the brake manipulation portion, and a brake caliper are connected with each other by a main brake passage. A first solenoid open/close valve, which changes over the communication and the interruption between the master cylinder and the brake caliper, is interposed in the main brake passage. A hydraulic modulator is connected to the main brake passage by way of a supply/discharge passage at a position closer to the brake caliper than the first solenoid open/close valve. Further, a reaction simulator, which applies a pseudo reaction to the brake manipulation portion when the first solenoid open/close valve is closed, is connected to the main brake passage by way of a branch passage at a position closer to the master cylinder than the first solenoid open/close valve. Further, in the respective vicinities of the master cylinder and the brake caliper, an input-side pressure sensor and an output-side pressure sensor are respectively disposed. The above-mentioned respective solenoid open/close valve and hydraulic modulator are controlled based on detection values of these sensors.
Further, in the brake device, the main brake passage is used as a backup passage when a system failure occurs. Thus, the respective first to third solenoid open/close valves are configured such that the main brake passage is opened in a non-electricity-supply state thus interrupting the branch passage and the supply/discharge passage. More specifically, a normally-open solenoid open/close valve is adopted as the first solenoid open/close valve which is interposed in the main brake passage, and a normally-closed solenoid open/close valve is adopted as the second and third solenoid open/close valves which are interposed in the branch passage and the supply/discharge passage.
In such a brake device which adopts the by-wire method, the brake device is required to cope with quick brake inputting from a rider. However, to always maintain the respective solenoid open/close valves in a standby state by supplying electricity to these solenoid open/close valves leads to an increase in power consumption. Thus, such a situation is not preferable with respect to the vehicle which is required to miniaturize a capacity of a generator or a battery.
Accordingly, in the above-mentioned brake device, the respective solenoid open/close valves are brought into a non-electricity-supply state during a period in which the brake manipulation portion is not manipulated and electricity is supplied to the respective solenoid open/close valves when the elevation of an inner pressure in a passage due to brake inputting is detected by an input-side pressure sensor.
In general, in a vehicle-use brake device, there may be a case in which a large liquid pressure equal to or more than a normally-used pressure acts on the whole brake system due to a phenomenon other than a brake manipulation purpose. Accordingly, respective portions in the brake system are required to possess the pressure proof performance capable of withstanding such a high pressure. At the same time, respective pressure sensors on an input side and an output side which detect the inner pressure in the passage are also required to possess the similar pressure proof performances.
However, the liquid pressure sensor which is generally used at present adopts the structure which converts a pressure change into a strain quantity and outputs an electric signal corresponding to the strain quantity. When the sensitivity of the liquid pressure sensor is set such that the liquid pressure sensor can perceive a fine pressure change immediately after starting the braking, the pressure proof performance against the high pressure is lowered. To the contrary, when the sensitivity of the pressure proof performance is set high against the high pressure, the resolution with respect to the fine pressure change immediately after starting braking is lowered.